Air conditioning (AC) is a collective expression for conditioning air into a desired state. It could be heating the air during cold periods, cooling the air during warmer periods or for cleaning the air if it contains unwanted particles. However, the expression air conditioning is most often used when emphasizing cooling. As a product, air conditioners can look and be used in various ways, but they all share the same basic technology.
Existing portable air-conditioners are often found to be large, hard to handle, noisy and inefficient. Furthermore, the connected exhaust air outlet that removes the heat from the room is often complicated and inefficient in its design. A known portable air-conditioner is for example described in the U.S. Pat. No. 2,234,753.
The design of portable AC systems differs from other Air Conditioners because all the components of the system are mounted inside of a packed unit which has to work inside of the conditioned space, releasing the residual energy (generated in the normal cooling process) through an air exhaust system which is usually connected to the outside.
In portable AC units there are two general procedures to cool down an air source condenser: single duct and dual duct methods. In the first one (single duct), the system takes air from its surroundings (conditioned space), forcing it to pass through the condenser surface and eventually removing the residual energy from it. Then, the hot air is expelled outdoors by using a single duct system. In this method, the intake air temperature has the indoor temperature conditions, which makes the energy exchange process more beneficial from standpoint of the refrigerant cycle.
In the dual duct method, the system uses an air intake duct to inject “hot” air from outdoor to cool down the condenser. Eventually the air coming from condenser at a relatively high temperature is released outdoors again by a secondary exhaust duct. In this method the air intake temperature is at the outdoor temperature conditions. This method can provide a quicker cooling effect for the user, since the system is not using the indoor air as a coolant media for condenser, but requiring in turn a larger size/volume of components to compensate the higher inlet outdoor temperatures.
Both methods, single and dual duct, have different limitations in terms of: air flow rates, size of the heat exchangers and also dimensions of the air piping system.
Those particularities requires that the portable AC systems make use of particular size of condensers, limiting the maximum air flow rate used by the system, since the air intake and air exhaust systems have to be as compact as possible.
Air flow rates in portable AC systems are also limited by the noise levels, since larger air flow rates flowing through small diameter hoses lead to higher pressure drops and higher noise levels. In that sense, the single duct systems have a clear advantage over the dual duct systems, because the temperature difference between the intake air and the condensing temperature of the cycle is larger, requiring lower air flow rates to perform the heat rejection process.
So, for portable AC systems, the condenser is one of the most critical components to design, since it has to exchange higher heat loads with a very limited air flow rate. Therefore, that particularity affects in a significant way the whole design of the condenser and the whole system performance.
On the other hand, evaporator is also an essential component to consider carefully in the design of portable AC systems, since this component has also similar limitations in terms of air flows and noise than air source condenser.
Additionally, the evaporator and its fan are the components of the system that interact directly with the conditioned space, since it is through those components that the system provides the cooling capacity to the indoors area. The importance of a good design of the evaporator lays in get the proper temperature distribution, humidity levels and air flow that in turn will affect the well-being and comfort of the users of the system.
For those reasons, the proper design of heat exchangers plays then an important role in the system performance. An optimum design of the heat exchanger geometries (internal and external), like the number of refrigeration circuits, the pipe connections and the heat exchanger size will affect the heat transfer processes and pressure drops, which will be critical for getting the optimum performance of the combined system.
There is a constant desire to improve the operation of air-conditioners.
Hence, there is a need for an improved air-conditioner.